Synthesis of microporous ceramics

Abstract

The present invention provides for microporous ceramic materials having a surface area in excess of 70 m2/gm and an open microporous cell structure wherein the micropores have a mean width of less than 20 Angstroms and wherein said microporous structure comprises a volume of greater than about 0.03 cm3/gm of the ceramic. The invention also provides for a preceramic composite intermediate composition comprising a mixture of a ceramic precursor and finely divided silicon carbide or silicon nitride, whose pyrolysis product in inert atmosphere or in an ammonia atmosphere at temperatures of up to less than about 1100 DEG C. gives rise to the microporous ceramics of the invention. Also provided is a process for the preparation of the microporous ceramics of the invention involving pyrolysis of the ceramic intermediate under controlled conditions of heating up to temperatures of less than 1100 DEG C. to form a microporous ceramic product.

What is claimed is: 
     
       1. A preceramic composite intermediate consisting essentially of a mixture of 52-70 parts by weight of a ceramic precursor oligomer having a number average molecular weight in the range of from about 200 to about 100,000 g/mole having uniformly dispersed therein 30-48 parts by weight of ceramic particles selected from the group consisting of silicon carbide, silicon nitride, silicon-carbide-nitride and mixtures thereof, said particles having a mean particle size or mean diameter of less than about 10 microns. 
     
     
       2. The composition of claim 1 wherein said ceramic precursor is selected from the group consisting of polysilazanes, polycarbosilazanes, perhydropolysilazanes, polycarbosilanes, vinylic polysilanes, amine boranes, polyphenylborazanes, carboranesiloxanes, polysilastyrenes, polytitanocarbosilanes, alumanes, polyalazanes and mixtures thereof. 
     
     
       3. The composition of claim 2 wherein said ceramic precursor is a polysilazane. 
     
     
       4. The composition of claim 2 wherein said ceramic precursor is a polycarbosilane. 
     
     
       5. The composition of claim 2 wherein said ceramic precursor is a polysilastyrene. 
     
     
       6. The composition of claim 1 which contains from about 52 to about 70 parts by weight of said ceramic precursor and from about 30 to about 48 parts by weight of said ceramic particles. 
     
     
       7. The composition of claim 1 wherein said ceramic particles comprise silicon carbide powder. 
     
     
       8. The composition of claim 1 wherein said ceramic particles comprise silicon nitride powder. 
     
     
       9. The composition of claim 1 wherein said ceramic particles comprise amorphous silicon-carbide-nitride.